Download What Is a Cell?

Lecture 3
Cell theory
By: Saba Nazeih
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• What Is a Cell?
• Living things are constructed of cells and can be unicellular (one
cell) or multicellular (many cells).
• Limits on Cell Size
• Cells size is limited because cells must be able to exchange materials
with their surroundings. In other words, surface area relative to the
volume decreases as size of cell increases, and this limits the size of
cells.
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• The CELL THEORY, or cell doctrine, states that all organisms are
composed of similar units of organization, called cells. The concept
was formally articulated in 1839 by Schleiden & Schwann and has
remained as the foundation of modern biology. The idea predates
other great paradigms of biology including Darwin's theory of
evolution (1859), Mendel's laws of inheritance (1865), and the
establishment
of
comparative
biochemistry
(1940).
Ultrastructural research and modern molecular biology have
added many tenets to the cell theory, but it remains as the
preeminent theory of biology. The Cell Theory is to Biology as
Atomic Theory is to Physics
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• He summarized his observations into three conclusions
about cells:
1) The cell is the unit of structure, physiology, and organization in
living things.
2) The cell retains a dual existence as a distinct entity and a
building block in the
construction of organisms.
3) Cells form by free-cell formation, similar to the formation of
crystals (spontaneous generation).
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• The modern tenets of the Cell Theory include:
1. All known living things are made up of cells.
2. The cell is structural & functional unit of all living things.
3. All cells come from pre-existing cells by division.
(Spontaneous Generation does not occur).
4. Cells contain hereditary information which is passed from
cell to cell during cell division.
5. All cells are basically the same in chemical composition.
6. All energy flow (metabolism & biochemistry) of life
occurs within cells.
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